Heterocycle sulfone oligomers and blends

ABSTRACT

High thermal stabilities are achievable in linear or multidimensional sulfone, solvent resistant oligomers by incorporating oxazole, thiazole, or imidazole linkages into the oligomer backbone. Blended oligomers of crosslinking oligomers and noncrosslinking compatible polymers are also described. The oligomers include residues of four-functional compounds of the formula: ##STR1## wherein M=--CO--, --S--, --O--, --SO 2  -- or --(CF 3 ) 2  C--; and 
     Y=--OH, --SH, or --NH 2 . 
     In an improved method, the reactants are condensed at or below ambient temperature in the presence of pyridine in a suitable solvent such as N,N&#39;-dimethylacetamide (DMAC).

REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application based upon U.S.Ser. No. 893,124, filed Aug. 4, 1986 now abandoned, which was acontinuation-in-part application based on U.S. Ser. No. 816,490, filedJan. 6, 1986 now abandoned, which was, in turn, a continuation-in-partapplication based upon U.S. Ser. No. 651,826, filed Sept. 18, 1984, nowabandoned.

TECHNICAL FIELD

The present invention relates to crosslinkable oligomers that includeoxazole, thiazole, or imidazole linkages along the oligomer backbonebetween mono- or difunctional crosslinking end-cap phenylimides, and tooligomer/polymer blends. The oligomers or blends are curable intocomposites (from prepregs) that exhibit improved solvent-resistance andthat have physical properties suitable for high performance, advancecomposites. The heterocycles include an electronegative (i.e. "sulfone")linkage on either side of each oxazole, thiazole, or imidazole linkage.

BACKGROUND ART

Recently, chemists have sought to synthesize oligomers for highperformance advanced composites suitable for aerospace applications.These composites should exhibit solvent resistance, be tough, impactresistant, and strong, be easy to process, and be thermoplastic.Oligomers and composites that have thermo-oxidative stability, and,accordingly can be used at elevated temperatures, are particularlydesirable.

While epoxy-based composites are suitable for many applications, theirbrittle nature and susceptibility to degradation make them inadequatefor many aerospace applications, especially those applications whichrequire thermally stable, tough composites. Accordingly, research hasrecently focused upon polyimide composites to achieve an acceptablebalance between thermal stability, solvent resistance, and toughness.The maximum use temperatures of conventional polyimide composites, suchas PMR-15, are still only about 600°-625° F., since they have glasstransition temperatures of about 690° F.

Linear polysulfone, polyether sulfone, polyester, and polyamide systemsare also known, but each of these systems fails to provide as highthermal stability as is required in some aerospace applications.

There has been a progression of polyimide sulfone compounds synthesizedto provide unique properties or combinations of properties. For example,Kwiatkowski and Brode synthesized maleic-capped, linear polyarylimidesas disclosed in U.S. Pat. No. 3,839,287. Holub and Evans synthesizedmaleic- or nadic-capped, imido-substituted polyester compositions asdisclosed in U.S. Pat. No. 3,729,446. We synthesized thermally stablepolysulfone oligomers as disclosed in U.S. Pat. No. 4,476,184 or4,536,559, and have continued to make advances withpolyetherimidesulfones, polybenzoxazolesulfones (i.e., heterocycles),polybutadienesulfones, and "star" or "star-burst" multidimensionaloligomers. We have shown surprisingly high glass transition temperaturesand desirable physical properties in many of these oligomers and theircomposites, without losing ease of processing.

Multidimensional oligomers, such as disclosed in our copendingapplications U.S. Ser. Nos. 726,258; 810,817; and 000,605, all nowabandoned, are easier to process than many other advanced compositeoligomers since they can be handled at lower temperatures. Upon curing,however, the unsaturated phenylimide end caps crosslink so that thethermal resistance of the resulting composite is markedly increased withonly a minor loss of stiffness, matrix stress transfer (impactresistance), toughness, elasticity, and other mechanical properties.Glass transition temperatures above 950° F. are achievable.

Commercial polyesters, when combined with well-known diluents, such asstyrene, do not exhibit satisfactory thermal and oxidative resistance tobe useful for aircraft or aerospace applications. Polyarylesters areunsatisfactory, also, since the resins often are semicrystalline whichmakes them insoluble in laminating solvents, intractable in fusion, andsubject to shrinking or warping during composite fabrication. Thosepolyarylesters that are soluble in conventional laminating solventsremain so in composite form, thereby limiting their usefulness instructural composites. The high concentration of ester groupscontributes to resin strength and tenacity, but also makes the resinsusceptible to the damaging effects of water absorption. High moistureabsorption by commercial polyesters can lead to distortion of thecomposite when it is loaded at elevated temperature.

High performance, aerospace, polyester advanced composites, however, canbe prepared using crosslinkable, endcapped polyester imide ether sulfoneoligomers that have an acceptable combination of solvent resistance,roughness, impact resistance, strength, ease of processing, formability,and thermal resistance. By including Schiff base (--CH═N--), imidazole,thiazole, or oxazole linkages in the oligomer chain, the linear,advanced composites formed with polyester oligomers of our copendingapplication U.S. Ser. No. 726,259 can have semiconductive or conductiveproperties when appropriately doped.

Conductive and semiconductive plastics have been extensively studied(see, e.g., U.S. Pat. Nos. 4,375,427; 4,338,222; 3,966,987; 4,344,869;and 4,344,870), but these polymers do not possess the blend ofproperties which are essential for aerospace applications. That is, theconductive polymers do not possess the blend of (1) toughness, (2)stiffness, (3) elasticity, (4) ease of processing, (5) impact resistance(and other matrix stress transfer capabilities), (6) retention ofproperties (over a broad range of temperatures), and (7) hightemperature resistance that is desirable on aerospace advancedcomposites. These prior art composites are often too brittle.

Thermally stable multidimensional oligomers having semiconductive orconductive properties when doped with suitable dopants are also knownand are described in our copending applications (including U.S. Ser. No.773,381 to Lubowitz, Sheppard, and Torre). The linear arms of theoligomers contain conductive linkages, such as Schiff base (--N═CH--)linkages, between aromatic groups. Sulfone and ether linkages areinterspersed in the arms. Each arm is terminated with a mono- ordifunctional end cap (i.e., a radical having one or two crosslinkingsites) to allow controlled crosslinking upon heat-induced orchemically-induced curing.

Polyamides of this same general type are described in our copendingpatent application U.S. Ser. No. 061,938; polyetherimides, in U.S. Ser.No. 016,703; and polyamideimides, in U.S. Ser. No. 092,740 nowabandoned.

SUMMARY OF THE INVENTION

The present invention relates to oxazole, thiazole, and imidazoleoligomers, particularly benzoxazole, benzothiazole, and benzimidazoleoligomers, capped with mono- or difunctional end-cap monomers (toprovide one or two crosslinking sites) to achieve superior thermalstability while retaining desirable strength and processing physicalproperties. Increased toughness is achieved by using electronegativelinkages, like --SO₂ --, on either side of the heterocycle linkages.

The linear heterocycle sulfone oligomers are usually prepared by thecondensation of:

(a) 2 moles of a phenylimide carboxylic acid halide end-cap monomer ofthe general formula: ##STR2## wherein D=a divalent radical that includeshydrocarbon unsaturation;

i=1 or 2; and

φ=phenyl

(b) n moles of a diacid halide, particularly an aromatic diacid halidehaving a plurality of aryl groups linked by "sulfone" linkages; and

(c) (n+1) moles of a four-functional "sulfone" compound of the formula:##STR3## wherein R has the formula: ##STR4##

M=--CO--, --SO₂ --, --(CF₃)₂ C--, --S--, or --O--; and

Y=--OH, --SH, or --NH₂. Isomers of the four-functional compound may alsobe used so long as the isomers include two pairs of an amine and a "Y"functionality on adjacent carbons on an aromatic radical.

The end-cap monomer preferably is selected from the group consisting of:##STR5## wherein D= ##STR6##

R₁ =lower alkyl, aryl, substituted aryl (including hydroxyl orhalo-substituents), lower alkoxy, aryloxy, halogen, or mixtures thereof(preferably lower alkyl);

X=halogen, preferably Cl;

i=1 or 2;

j=0, 1, or 2;

G=--CH₂ --, --O--, --S--, or --SO₂ --

φ=phenyl;

T=methallyl or allyl; and

Me=methyl. Preferred end-cap monomers are the phenylimide halideswherein D= ##STR7## wherein R" is hydrogen or lower alkyl.

Preferred oligomers have an average formula weight between about 500 andabout 30,000; more preferably, between about 1,000 to 20,000; and mostpreferably, between about 1,000 to 5,000.

The oligomers are made by condensing the reactants from a threecomponent mixture in a suitable solvent under an inert atmosphere.

Blended oligomers are prepared to include the crosslinking oligomers anda compatible polymer that usually has a comparable or a substantiallyidentical backbone, but that is terminated or quenched with a monomerthat is unable to crosslink when the blend is heated or treated withchemical curing initiators (such as organic peroxides). Accordingly, thecomparable oligomer usually is prepared by condensing:

(a) 2 moles of an acid halide momomer;

(b) n moles of the diacid halide of the crosslinking oligomer;

(c) (n+1) moles of the four-functional "sulfone" reactant of thecrosslinking oligomer, wherein n≧1. A suitable monomer for quenching thepolymerization reaction for the comparable oligomer is benzoic acidhalide ##STR8##

Of course, the oligomers can also be prepared by the condensation of:

(a) 2 moles of a suitable phenylimide amine, phenol, or thiol(sulfhydryl) monomer;

(b) n moles of a four-functional compound; and

(c) (n+1) moles of a suitable diacid halide.

The compatible polymer in this case would also usually include theanalogous backbone and could be quenched with a phenol compound orsuitable thio- or amino-monomer (such as aniline).

Oligomers of this general type are easily processed into prepregs andcomposites. The composites (or laminates) are chemically, thermally, anddimensionally stable, are tough, can withstand relatively hightemperatures, and are resistant to solvents generally found in aerospaceapplications.

An improved method for synthesizing these oligomers in the presence ofpyridine is also described and claimed.

BEST MODE CONTEMPLATED FOR CARRYING OUT THE INVENTION

The crosslinking oligomers of the present invention are oxazoles,thiazoles, or imidazoles prepared by the condensation of:

(a) 2 moles of an unsaturated phenylimide carboxylic acid halide end-capmonomer;

(b) n moles of a diacid haide, particularly an aromatic diacid halidehaving a plurality of aryl groups linked by "sulfone" (i.e.electronegative) linkages; and

(c) (n+1) moles of a four-functional "sulfone" compound of the formula:##STR9## wherein R is a hybrocarbon radical selected from the groupconsisting of:

M=--CO--, SO₂ --, --(CF₃)₂ C--, --S--, or --O--; and

Y=--OH, --SH, or --NH₂.

The end-cap monomer generally is selected from the group consisting of:##STR10## wherein D= ##STR11##

R₁ =lower alkyl, aryl, substituted aryl (including hydroxyl orhalo-substituents), lower alkoxy, aryloxy, halogen, or mixtures thereof(preferably lower alkyl);

X=halogen;

φ=phenyl;

G=--O--, --S--, --SO₂ -- or --CH₂ --;

i=1 or 2;

j=0, 1, or 2;

T=methallyl or allyl; and

Me=methyl. The unsaturation provides a crosslinking site upon thermal orchemical curing to form a composite.

Particularly preferred end-caps (for the highest thermal stability)include: ##STR12## wherein D= ##STR13## and R" is hydrogen or loweralkyl.

The reaction is generally carried out at ambient conditions or belowunder an inert atmosphere (dry N₂ purge) in a suitable solvent includingan excess of base (pyridine) to eliminate the possibility of undesirableside reactions that might otherwise occur in an acidic solution.Pyridine is preferred over other bases, such as NaOH or KOH.

The dicarboxylic acid halide (or dicarboxylic acid) may include anaromatic chain segment selected from the group consisting of:

(a) phenyl;

(b) naphthyl;

(c) biphenyl;

(d) a polyaryl "sulfone" divalent radical of the general formula:##STR14## wherein

D=--S--, --O--, --CO--, --SO₂ --, --(CH₃)₂ C--, --(CF₃)₂ C--, ormixtures thereof throughout the chain; or

(e) a divalent radical having conductive linkages, illustrated by Schiffbase compounds selected from the group consisting of: ##STR15## whereinR is selected from the group consisting of: phenyl; biphenyl; naphthyl;or a divalent radical of the general formula: ##STR16## wherein W=--SO₂-- or --CH₂ --; and q=0-4; or (f) a divalent radical of the generalformula: ##STR17## wherein R¹ =a C₂ to C₁₂ divalent aliphatic,alicyclic, or aromatic radical, and, preferably, phenyl (as described inU.S. Pat. No. 4,556,697).

Thiazole, oxazole, or imidazole linkages, especially between arylgroups, may also be used instead of the Schiff base linkages. Theoligomers, already being heterocycles, may be semiconductive upon dopingeven without incorporating additional conductive linkages.

The diacid halide (i.e. dicarboxylic acid halide or the acid) then ispreferably selected from the group consisting of: ##STR18## wherein q is--CO--, --S--, --(CF₃)₂ C--, or --SO₂ --, and, most preferably, --CO--or --SO₂ --, and acid halides represented by the formula: ##STR19##wherein q=an electronegative ("sulfone") linkage (--SO₂ --, --S--,--CO--, or --(CF₃)₂ C--) as previously defined, and m=an integer,generally from 1-5.

The most preferred acid halides include: ##STR20##

Schiff base dicarboxylic acids and diacid haides can be prepared by thecondensation of aldehydes and aminobenzoic acid (or other amine acids)in the general reaction scheme: ##STR21## or similar syntheses.

Other diacid halides that can be used, but that are not preferred, aredisclosed in U.S. Pat. No. 4,504,632, and include: adipylchloride,malonyl chloride, succinyl chloride, glutaryl chloride, pimelic aciddichloride, suberic acid dichloride, azelaic acid dichloride, sebacicacid dichloride, dodecandioic acid dichloride, phthaloyl chloride,isophthaloyl chloride, terephthaloyl chloride, 1,4-naphthalenedicarboxylic acid dichloride, and 4,4'-diphenylether dicarboxylic aciddichloride.

Polyaryl or aryl diacid halides are preferred to achieve the highestthermal stabilities in the resulting oligomers and composites becausealiphatic bonds are not as thermally stable as aromatic bonds.Particularly preferred compounds include intermediate "sulfone" (i.e.electronegative) linkages to improve the toughness of the resultingoligomers. For purposes of this description, "sulfone" linkages shouldbe understood to include --SO₂ --, --S--, --CO--, and --(CF₃)₂ C--,unless clearly limited to only --SO₂ --.

Suitable diacid halides include compounds made by reacting nitrobenzoicacid with a bisphenol (i.e., dihydric phenol, dialcohol, or diol). Thebisphenol is preferably selected from the group consisting of:2,2-bis-(4-hydroxyphenyl)-propane (i.e., bisphenol-A);bis-(2-hydroxyphenyl)-methane; bis-(4-hydroxyphenyl)-methane;1,1-bis-(4-hydroxyphenyl)-ethane; 1,2-bis-(4-hydroxyphenyl)-ethane;1,1-bis-(3-chloro-4-hydroxyphenyl)-ethane;1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-ethane;2,2-bis-(3-phenyl-4-hydroxyphenyl)-propane;2,2-bis-(4-hydroxynaphthyl)-propane 2,2-bis-(4-hydroxyphenyl)-pentane;2,2-bis-(4-hydroxyphenyl)-hexane; bis-(4-hydroxyphenyl)-phenylmethane;bis-(4-hydroxyphenyl)-cyclohexylmethane;1,2-bis-(4-hydroxyphenyl)-1,2-bis-(phenyl)-ethane;2,2-bis-(4-hydroxyphenyl)-1-phenylpropane;bis-(3-nitro-4-hydrophenyl)-methane;bis-(4-hydroxy-2,6-dimethyl-3-methoxyphenyl)-methane;2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane;2,2-bis-(3-bromo-4-hydroxyphenyl)-propane; or mixtures thereof, asdisclosed in U.S. Pat. No. 3,262,914. Bisphenols having aromaticcharacter (i.e., absence of aliphatic segements), such as bisphenol-A,are preferred.

The bisphenol may be in phenate form, or a corresponding sulfyhydryl canbe used. Of course, mixtures of bisphenols and disulfhydryls can beused.

Other suitable bisphenols are described in our copending applications016,703 and 726,258; or in U.S. Pat. Nos. 4,584,364; 4,661,604;3,262,914, or 4,611,048.

While bisphenol-A ispreferred (because of cost and availability), theother bisphenols can be used to add rigidity to the oligomer withoutsignificantly increasing the average formula weight, and therefore, canincrease the solvent resistance. Random or block copolymers arepossible.

Bisphenols of the type described are commercially available. Some may beeasily synthesized by reacting dihalogen intermediate with bis-phenates,such as the reaction of 4,4'-dichlorophenyl-sulfone with bis(disodiumbiphenolate). Preferred dihalogens in this circumstance are selectedfrom the group consisting of: ##STR22## wherein

X=halogen, preferably chlorine; and

q=--S--, --SO₂ --, --(CO--, --(CH₃)₂ C--, and --(CF₃)₂ C--, andpreferably either --SO₂ -- or --CO--.

The heterocycle oligomers of the present invention can also be preparedby the condensation of:

(a) 2 moles of a crosslinking phenylimide amine, phenol, or sulfhydrylend-cap monomer;

(b) n moles of the four-functional compound; and

(c) (n+1) moles of a suitable diacid halide.

In this case, the end-cap monomer generally has the formula: ##STR23##wherein D, i, and φ are as previously defined and Y=--OH, --SH, or--NH₂.

Blends can improve impact resistance of composites without causing asignificant loss of solvent resistance. The blends comprise mixtures ofone or more crosslinkable oligomer and one or more polymer that isincapable of crosslinking. Generally, the blends comprise substantiallyequimolar amounts of one polymer and one oligomer having substantiallyidentical backbones. The crosslinkable oligomer and compatible polymercan be blended together by mixing mutually soluble solutions of each.While the blend is preferably equimolar in the oligomer and polymer, theratio of the oligomer and polymer can be adjusted to achieve the desiredphysical properties.

Although the polymer in such a blend usually has the same lengthbackbone as the oligomer, the properties of the composite formed fromthe blend can be adjusted by altering the ratio of formula weights forthe polymer and oligomer. The oligomer and polymer generally havesubstantially identical repeating units, but the oligomer and polymermerely need be compatible in the solution prior to sweeping out as aprepreg. Of course, if the polymer and oligomer have identicalbackbones, compatibility in the blend is likely to occur. Blends thatcomprise relatively long polymers and relatively short oligomers (i.e.,polymers having higher average formula weights than the oligomers) priorto curing are preferred, since, upon curing, the oligomers willeffectively increase in MW by crosslinking.

In synthesizing the comparable polymers, quenching end caps can beemployed, if desired, to regulate the polymerization of the comparablepolymer, so that it has an average formula weight substantiallyidentical with the crosslinkable oligomer. For thermal stability, anaromatic compound, such as aniline or benzoic acid chloride, ispreferred to quench the synthesis.

Solvent resistance may decrease markedly if the comparable polymer isprovided in large excess to the crosslinkable oligomer in the blend.

The blends will generally comprise a mixture of a heterocycle oligomerand the same heterocycle polymer (i.e., oxazole oligomer and oxazolepolymer). The polymer may, however, be a different heterocycle, such asan imide, imidazole, or thiazole. The mixture may include several typesof oligomers or several types of polymers, such as a three componentmixture of an oxazole oligomer, a thiazole oligomer, and an imidazolepolymer.

The blends may be semi-interpenetrating networks of the general typedescribed by Egli et al. "Semi-Interpenetrating Networks of LARC-TPI"available from NASA-Langley Research Center.

The average formula weight of the preferred crosslinking oligomersranges between about 500 and about 30,000; preferably between about1,000 and about 20,000; and (for thermosetting compositions) still morepreferably between about 1,000 and 5,000. Mixtures of crosslinkingoligomers having molecular weights within these ranges may also be used,for example, a mixture of an oligomer having a molecular weight of about1,000 with an oligomer having a molecular weight of about 20,000, or amixture of an oligomer with a molecular weight of about 5,000 with anoligomer having a molecular weight of about 10,000 or about 20,000.Within the described ranges, the oligomers can be crosslinked to formsolvent resistant composites of high thermal stability suitable for manyaerospace applications. The oligomers, however, are relatively soluble,and, therefore, may be easily processed into prepregs by conventionalsteps.

Generally, for making linear heterocycles, the diacid halide is selectedfrom the group consisting of: ##STR24## wherein q is selected from thegroup consisting of --(CF₃)₂ C--, --SO₂ --, --S--, or --CO--; X isselected from the group consisting of --O-- or --SO₂ --; E, E₁, E₂ andE₃ each represent substituent groups selected from the group consistingof halogen, alkyl groups having 1 to 4 carbon atoms, and alkoxy groupshaving 1 to 4 carbon atoms, and "a," "b," "c," and "d" are all integershaving values from 0 to 4.

The compound: ##STR25## is particularly preferred, especially if theend-cap monomer is either: ##STR26##

Prepregs and composites of these oligomers can be prepared byconventional techniques. Suitable prepreging reinforcements includeceramic, organic (including KEVLAR), carbon, and glass fibers incontinuous, woven or chopped form. The composites may be cured fromprepregs or might be filled oligomers. Curing temperatures might besomewhat higher than those used on commodity oligomers, but the curingprocess will be readily understood by those of ordinary skill in theart.

The four-functional compounds and diacid halides are commerciallyavailable from Hoescht or Burdick & Jackson, or are readily preparedfrom these commercial compounds.

Multidimensional oligomers may be synthesized using an aromatic hub,such as cyuranic acid (or its acid halide), the four-functionalcompounds, and the acid halide end-cap monomers. The oligomers have thegeneral formula:

    AR(T).sub.w

wherein

Ar=the aromatic hub residue;

T=a monovalent radical having at least two heterocyclic (oxazole,thiazole, or imidazole) linkages, at least one "sulfone" linkage, and atleast one terminal, crosslinking functionality thereby having thegeneral formula: ##STR27## wherein M, D, φ, and i are as previouslydefined;

a=a heterocycle linkage;

D₁ =a residue of a diacid halide;

p=an integer, generally from 1-5, and

n=0 or 1, if p=1, or 1, if p>1; and

w=an integer greater than or equal to 3, and preferably 3 or 4.

The chains can be further extended by including a diacid halide residuebonded to the hub.

In multidimensional oligomers, an aromatic hub includes a plurality ofrays or spokes radiating from the hub in the nature of a star to providemultidimensional crosslinking through suitable terminal groups with agreater number (i.e. higher density) of crosslinking bonds than lineararrays provide. Usually the hub will have three radiating chains to forma "Y" pattern. In some cases, four chains may be used. Including morechains leads to steric hindrance as the hub is too small to accommodatethe radiating chains. A trisubstituted phenyl hub is highly preferredwith the chains being symmetrically placed about the hub. Biphenyl,naphthyl, or azaline (e.g., melamine) may also be used as the hubradical along with other aromatic moieties, if desired.

Triazine derivatives can be used as the hub. These derivatives aredescribed in U.S. Pat. No. 4,574,154 and have the general formula:##STR28## wherein R₂ is a divalent hydrocarbon residue containing 1-12carbon atoms (and, preferably, ethylene) by reacting the aminefunctionalities with phthalic acid anhydride to form arms that includeimide linkages and terminal acid functionalities (that can be convertedto acid halides, if desired). The triazine derivatives of U.S. Pat. No.4,617,390 (or the acid halides) can also be used as the hub.

Hubs suitable for making multidimensional, heterocycle oligomers of thepresent invention can be made by reacting polyol aromatic hubs, such asphloroglucinol, with nitrobenzoic acid or nitrophthalic acid to formether linkages and active, terminal carboxylic acid functionalities. Thenitrobenzoic acid products would have three active sites while thenitrophthalic acid products would have six; each having the respectiveformula:

    φ[O--φ--COOH].sub.3 or φ[O--φ--(COOH).sub.2 ].sub.3

wherein φ=phenyl. Of course other nitro/acids can be used.

Hubs can also be formed by reacting the corresponding halo-hub (such atribromobenzene) with aminophenol to form triamine compounds representedby the formula: ##STR29## which can then be reacted with an acidanhydride to form a polycarboxylic acid of the formula: ##STR30##wherein φ=phenyl; the hub being characterized by an intermediate etherand imide linkage connecting aromatic groups. Thio-analogs are alsocontemplated, in accordance with U.S. Pat. No. 3,933,862.

Phenoxyphenyl sulfone arms radiating from a hub with either an amine orcarboxylic acid are also precursors for making multidimensionalheterocycle oligomers of the present invention.

The best results are likely to occur when the hub is cyanuric acid, andwhen a four-functional compound and end-cap monomer are reacted with thehub to form a short armed oligomer having three or six crosslinkingsites. These compounds are the simplest multidimensional oligomers andare relatively inexpensive to synthesize.

Blends of the multidimensional oligomers, comparable to the blends oflinear oligomers, can also be prepared, as will be understood.

The oligomers can be synthesized in a homogeneous reaction schemewherein all the reactants are mixed at one time, or in a stepwisereaction scheme wherein the radiating chains are affixed to the hub andthe product of the first reaction is subsequently reacted with the endcap groups. Of course, the hub may be reacted with end-capped arms thatinclude one reactive, terminal functionality for linking the arm to thehub. Homogeneous reaction is preferred, resulting undoubtedly in amixture of oligomers because of the complexity of the reactions. Theproducts of the processes (even without distillation or isolation ofindividual species) are preferred oligomer mixtures which can be usedwithout further separation to form the desired advanced composites.

If the linear or multidimensional oligomers include Schiff base or otherconductive linkages, the composites may be conductive or semiconductivewhen suitably doped. The dopants are preferably selected from compoundscommonly used to dope other polymers, namely, (1) dispersions of alkalimetals (for high activity) or (2) strong chemical oxidizers,particularly alkali perchlorates (for lower activity). Arsenic compoundsand elemental halogens, while active dopants, are too dangerous forgeneral usage, and are not recommended.

The dopants apparently react with the oligomers or polymers to formcharge transfer complexes. N-type semiconductors result from doping withalkali metal dispersions. P-type semiconductors result from doping withelemental iodine or perchlorates. Dopant should be added to the oligomeror blend prior to forming the prepreg.

While research into conductive or semiconductive polymers has beenactive, the resulting compounds (mainly polyacetylenes, polyphenylenes,and polyvinylacetylenes) are unsatisfactory for aerospace applicationsbecause the polymers are:

(a) unstable in air;

(b) unstable at high temperatures;

(c) brittle after doping;

(d) toxic because of the dopants; or

(e) intractable.

These problems are overcome or significantly reduced with the conductiveoligomers of the present invention.

While conventional theory holds that semiconductive polymers should have(1) low ionization potentials, (2) long conjugation lengths, and (3)planar backbones, there is an inherent trade-off between conductivityand toughness or processibility, if these constraints are followed. Toovercome the processing and toughness shortcomings common with Schiffbase, oxazole, imidazole, or thiazole polymers, the oligomers of thepresent invention generally include "sulfone" linkages interspersedalong the backbone providing a mechanical swivel for the rigid,conductive segments of the arms.

Because the heterocycle (oxazole, thiazole, or imidazole) linkages arethemselves within the family of conductive or semiconductive linkages,it may be unnecessary to include Schiff base linkages to achieveconductive or semiconductive properties upon doping. That is, conductiveor semiconductive properties might be achieved simply be doping theoxazole, thiazole, or imidazole oligomers.

Linear or multidimensional oligomers can be synthesized from a mixtureof four or more reactants so that extended chains may be formed. Addingcomponents to the reaction mixture, however, adds to the complexity ofthe reaction and of its control. Undesirable competitive reactions mayresult or complex mixtures of macromolecules having widely differentproperties may be formed, because the chain extenders and chainterminators are mixed, and compete with one another.

While para isomerization is shown for all of the reactants, otherisomers are possible. Furthermore, the aryl groups can havesubstituents, if desired, such as halogen, lower alkyl up to about 4carbon atoms, lower alkoxy up to about 4 carbon atoms, or aryl.Substituents may create steric hindrance problems in synthesizing theoligomers or in crosslinking the oligomers into the final composites.

The heterocycle oligomers of the present invention are distinguishedfrom those of our earlier applications by the four-functional compounds.Here, those compounds include an intermediate "sulfone" linkage toprovide a mechanical swivel within the backbone or the oligomers.Because the heterocycle linkages are rigid or stiff, the incorporationof these electronegative ("sulfone") linkages improves the toughness ofthe resulting composites without significant decrease of the otherphysical properties. While our heterocycles in general are improvementsover pure heterocycles by the use of electronegative linkages in thediacid halide residues, the special subclass of the present invention isbelieved to provide even betteer physical properties beneficial forstructural aerospace applications. On either side of the rigidheterocycle linkages in the backbone, the electronegative ("sulfone")linkages provide stress relief. Our earlier heterocycle oligomers didnot necessarily include an electronegative linkage within thefour-functional compound.

Prepregs of the oligomers or blends can be prepared by conventionaltechniques. While woven fabrics are the typical reinforcement, thefibers can be continuous or discontinuous (in chopped or whisker form)and may be ceramic, organic, carbon (graphite), or glass, as suited forthe desired application.

Composites can be formed by curing the oligomers or prepregs inconventional vacuum bag techniques. The oligomers can also be used asadhesives, varnishes, films, or coatings.

The following examples are presented to illustrate various features ofthe invention.

EXAMPLE I Synthesis of bis(3-methylphenoxyphenyl)sulfone ##STR31##

A one liter bottle fitted with a stirrer, thermometer, Barrett,condenser, and nitrogen inlet tube was charged with 88.3 grams (0.82moles) of m-cresol, 286.6 grams of dimethyl sulfoxide (DMSO), 134.8grams of toluene, and 65.3 grams of a 50% NaOH solution. The mixture washeated to 127° C. and the water was removed. The mixture was then heatedto 165° C. to remove the toluene, and was cooled to 110° C. beforeadding 111.7 grams (0.39 moles) of dichlorodiphenylsulfone. The mixturewas heated for 4 hours at 141° C., before the mixture was poured into 3liters of water to crystalize an intermediate. The water wasdecanted,and 1 liter of 2-propanol was added. This mixture was heated until themajority of the product dissolved. The product was recrystallized,recovered by filtration, washed with 3 liters of water followed by 500ml of 2-propanol, and dried. 167.4 grams of abis(2-methylphenoxyphenyl)sulfone product resulted. The melting pointranged from 83°-85° C.

EXAMPLE II Synthesis of bis(3-carboxyphenoxyphenyl)sulfone ##STR32##

A reaction flask fitted with a stirrer, condenser, thermometer, andN₂purge was charged with 100 grams of the product of Example I, 775grams of pyridine, and 155 grams of water. The mixture was refluxed andoxidized with 49 grams of KMnO₄, filtered to recover the intermediate towhich775 grams of 1.8N NaOH solution was added. The mixture wasrefluxed, oxidized, and filtered again. The oxidation steps wererepeated 5 times. The resulting final product had a melting pointranging from about 213.5° to 219° C.

EXAMPLE III Synthesis of the acid chloride of the product obtained inExample II ##STR33##

Twenty grams of the product of Example II was mixed with 61.2 grams ofSOCl₂ in a reaction flask, fitted with a stirrer, condenser,thermometer, and dry-N₂ purge. The mixture was refluxed for 2 hours andthe SOCl₂ was distilled off. 200 milliliters of benzene was addedand themixture was refluxed, cooled, and filtered to recover the raw productwhich was recrystallized to a powder. The powder was mixed with 200milliliters of benzene, refluxed, and cooled to form a precipitate thathad a melting range of about 115° to 118° C.

EXAMPLE IV Synthesis of nadic dicapped benzoxazole

In a flask equipped with a nitrogen purge and a mechanical stirrer, 9.34g (0.043 moles) of 3,3'-dihydroxybenzidine was mixed with 34.2 gpyridine and 31 g N,N'-dimethylacetamide. The mixture was stirred in anice water bath until the mixture temperature reached 10° C. Then, 11.39g (0.0216 moles) of bis(4-carboxyphenoxyphenylsulfone and 20.0 g (0.043moles) 3,5' dinadicimidobenzoyl chloride in 126 gN,N'-dimethylacetamide. Stirring continued for 4 hours followingcompletion of the addition of thereactants. A product was recovered bypouring the reaction mixture into water and blending the resultingmixture. Residual hydrochloride salts were removed from the recoveredproduct (after filtering) by washing the product thoroughly with waterbefore drying the product at 100° C. The yield was nearly quantitative.

EXAMPLE V Synthesis of nadic dicapped benzoxazole

Approximately 10.6 mmoles of acid chloride terminated sulfone of ExampleIII is mixed with about 5.3 mmoles of nadic dicapped acid chloride inmethylenedichloride and a suitable base (pyridine). The resultingmixture is added with an addition funnel to a stirred slurry containingabout 13.0mmoles of a four-functional compound of the formula:##STR34##in DMAC to form a reaction mixture. After stirring for 3 hoursat room temperature under an inert atmosphere, the stirring is stoppedand the mixture is allowed to sit at room temperature for about 48hours. The oligomer is recovered in methylenedichloride, and isrecrystallized using petroleum ether. The oligomer is washed withpetroleum ether and, then, with methanol.

While preferred embodiments have been described, those skilled in theart will recognize alterations, variations, or modifications that mightbe made to the embodiments without departing from the inventive concept.The description and examples, accordingly, are meant to illustrate theinvention. The claims should be interpreted liberally in view of thedescription, and should be limited only as is necessary in view of thepertinent prior art.

We claim:
 1. A crosslinkable heterocycle sulfone oligomer formed byreacting:(a) 2 moles of an unsaturated, crosslinking, phenylimidecarboxylic acid halide of the general formula: ##STR35## wherein D=adivalent radical that includes hydrocarbon unsaturation such that##STR36## is a radical selected from the group consisting of: ##STR37##2. The oligomer of claim 1 wherein the terminal carboxylic acid halidefunctionalities of the diacid halide are attached at the ends of ahydrocarbon residue selected from the group consisting of:(a) phenyl;(b) naphthyl; (c) biphenyl; (d) a polyaryl divalent radical of thegeneral formula: ##STR38## wherein D¹ =--S--, --O--, --CO--, --SO₂ --,--(CH₃)₂ C--, --(CF₃)₂ C--, or mixtures thereof throughout the chain;(e) a divalent radical having conductive linkages, illustrated by Schiffbase compounds selected from the group consisting of: ##STR39## whereinR is selected from the group consisting of: phenyl; biphenyl; naphthyl;or a divalent radical of the general formula: ##STR40## wherein W=--SO₂-- or --CH₂ --; and q=0-4; or (f) a divalent radical of the generalformula: ##STR41## wherein R¹ =a C₂ to C₁₂ divalent aliphatic,alicyclic, or aromatic radical.
 3. The oligomer of claim 1 wherein thediacid halide is selected from the group consisting of: ##STR42##wherein q=--SO₂ --, --S--, --CO--, or --(CF₃)₂ C--; andm=0-5.
 4. Theoligomer of claim 3 wherein the diacid halide is ##STR43## whereinφ=phenyl.
 5. The oligomer of claim 1 wherein the diacid halide has theformula: ##STR44## wherein q is selected from the group consisting of:

    --(CF.sub.3).sub.2 C--, --SO.sub.2 --, --S--, or --CO--;

x is selected from the group consisting of --O-- and --SO₂ --; E, E₁, E₂and E₃ each represent substituent groups selected from the groupconsisting of halogen, alkyl groups having 1 to 4 carbon atoms, andalkoxy groups having 1 to 4 carbon atoms; and "a", "b", "c", and "d"each is an integer having a value of 0 to
 4. 6. The oligomer of claim 5wherein q is --SO₂ -- and a=b=c=d=0.
 7. A prepreg comprising theoligomer of claim 2 and a reinforcing additive in fiber or particulateform.
 8. A composite formed by curing the prepreg of claim
 7. 9. Acomposite formed by curing the oligomer of claim
 2. 10. A method formaking a heterocycle oligomer comprising the step of:condensingsimultaneously a mixture of (i) 2 moles of a phenylimide end-cap monomerof the general formula: ##STR45## wherein D=a divalent radical thatincludes hydrocarbon unsaturation; ##STR46## is a radical selected fromthe group consisting of: ##STR47## wherein R₁ =lower alkyl, loweralkoxy, aryl, aryloxy, substituted alkyl, substituted aryl, halogen, ormixtures thereof;j=0, 1, or 2; G=--CH₂ --, --O--, --S--, or --SO₂ --;T=methallyl or allyl; Me=methyl; i=1 or 2; φ=phenyl; and Y=--OH, --SH,or --NH₂, (ii) about w moles of a four-functional compound of thegeneral formula: ##STR48## wherein R= ##STR49## and

    M=--CO--, --S--, --O--, --SO.sub.2 --, or --(CF.sub.3).sub.2 C--, and

(iii) about (w+1) moles of a diacid halide that includes terminalcarboxylic acid halide functionalities, the condensation occurring in asuitable solvent in the presence of pyridine under an inert atmosphereat ambient temperature or below.
 11. The product of the process of claim10.
 12. The product of claim 11 wherein the diacid halide includesterminal carboxylic acid halide functionalities that are attached at theends of a hydrocarbon residue selected from the group consisting of:(a)phenyl; (b) naphthyl; (c) biphenyl; (d) a polyaryl divalent radical ofthe general formula: ##STR50## wherein D¹ =--S--, --O--, --CO--, --SO₂--, --(CH₃)₂ C--, --(CF₃)₂ C--, or mixtures thereof throughout thechain; (e) a divalent radical having conductive linkages, illustrated bySchiff base compounds selected from the group consisting of: ##STR51##wherein R₂ is selected from the group consisting of: phenyl; biphenyl;naphthyl; or a divalent radical of the general formula: ##STR52##wherein W=--SO₂ --, or --CH₂ --; and q=0-4; or (f) a divalent radical ofthe general formula: ##STR53## wherein R¹ =a C₂ to C₁₂ divalentaliphatic, alicyclic, or aromatic radical; and ##STR54## is a radicalselected from the group consisting of: ##STR55## wherein R₁ =loweralkyl, lower alkoxy, aryl, aryloxy, substituted alkyl, substituted aryl,halogen, or mixtures thereof; j=0, 1, or 2; G=--CH₂ --, --O--, --S--, or--SO₂ --; T=methallyl or allyl; and Me=methyl.
 13. The product of claim12 wherein the diacid halide is selected from the group consisting of:##STR56## wherein q=--SO₂ --, --S--, --CO--, or --(CF₃)₂ C--; andm=0-5.14. The product of claim 12 wherein Y=--OH.
 15. The product of claim 12wherein Y=--SH.
 16. The product of claim 12 wherein Y=--NH₂.
 17. Amethod for making a multidimensional heterocycle sulfone oligomercomprising the step of:condensing simultaneously a mixture that includes(i) a hub of the general formula Ar(COX)_(w) wherein Ar=any aromaticradical of valence w, X=halogen, and w=an integer greater than or equalto 3, (ii) about w moles of a four-functional compound of the generalformula: ##STR57## wherein Y=--OH, --SH, or --NH₂ ; ##STR58## and

    M=--CO--, --S--, --O--, --SO.sub.2 --, or --(CF.sub.3).sub.2 C--

and (iii) about w moles of a phenylimide carboxylic acid halide of thegeneral formula: ##STR59## wherein D=a divalent radical that includeshydrocarbon unsaturation; ##STR60## is a radical selected from the groupconsisting of: ##STR61## wherein R₁ =lower alkyl, lower alkoxy, aryl,aryloxy, substituted alkyl, substituted aryl, halogen, or mixturesthereof; j=0, 1, or 2; G=--CH₂ --, --O--, --S--, or --SO₂ --;T=methallyl or allyl; Me=methyl; i=1 or 2; and φ=phenyl,the condensationoccurring in a suitable solvent in the presence of pyridine under aninert atmosphere.
 18. The method of claim 17 wherein the condensationoccurs at ambient temperature or below.
 19. The product of the processof claim
 17. 20. The product of claim 19 wherein Y=--OH.
 21. The productof claim 19 wherein Y=--SH.
 22. The product of claim 19 wherein Y=--NH₂.23. A heterocycle sulfone oligomer of the general formula: ##STR62##wherein E=an end-cap monomer of the general formula:

    [D].sub.i φ--

i=1 or 2; φ=phenyl; D=a radical selected from the group consisting of:##STR63## R₁ =lower alkyl, lower alkoxy, aryl, aryloxy, substitutedalkyl, substituted aryl, halogen, or mixtures thereof; j=0, 1, 2;G=--CH₂ --, --O--, --S--, or --SO₂ --; T=methallyl or allyl; Me=methyl;A= ##STR64## M=--CO--, --S--, --O--, --SO₂ --, or --(CF₃)₂ C--; B=aresidue of a dicarboxylic acid halide that includes the carboxylic acidhalide functionalities attached to the ends of a hydrocarbon residueselected from the group consisting of:(a) phenyl; (b) naphthyl; (c)biphenyl; (d) a polyaryl divalent radical of the general formula:##STR65## wherein D¹ =--S--, --O--, --CO--, --SO₂ --, --(CH₃)₂ C--, ormixtures thereof throughout the chain; (e) a divalent radical havingconductive linkages, illustrated by Schiff base compounds selected fromthe group consisting of: ##STR66## wherein R₂ is selected from the groupconsisting of: phenyl; biphenyl; naphthyl; or a divalent radical of thegeneral formula: ##STR67## wherein W=--SO₂ --, or --CH₂ --; and q=0-4;or (f) a divalent radical of the general formula: ##STR68## wherein R¹=a C₂ to C₁₂ divalent aliphatic, alicyclic, or aromatic radical; a=aheterocycle linkage selected from the group consisting of oxazole,thiazole, or imidazole; and m=an integer so that the oligomer has anaverage formula weight greater than about 500; ##STR69## wherein R₁=lower alkyl, lower alkoxy, aryl, aryloxy, substituted alkyl,substituted aryl, halogen, or mixtures thereof; i=1 or 2 X=halogen; j=0,1, or 2; G=--CH₂ --, --O--, --S--, or --SO₂ --; T=methallyl or allyl;and Me=methyl;(b) n moles of diacid halide that includes terminalcarboxylic acid halide functionalities; and (c) n+1 moles of at leastone four-functional compound of the general formula: ##STR70## wherein Ris selected from the group consisting of compounds of the generalformula: ##STR71## wherein M=--CO--, --SO₂ --, --(CF₃)₂ C--, --S--, or--O--; Y is selected from the group consisting of --OH, --SH, and --NH₂; and n is selected so that the oligomer has an average formula weightgreater than about
 500. 24. The heterocycle sulfone oligomer of claim 23wherein D is selected from the group consisting of: ##STR72## and R" ishydrogen or lower alkyl.
 25. The heterocycle sulfone oligomer of claim23 wherein B=a residue of a dicarboxylic acid halide selected from thegroup consisting of: ##STR73##
 26. A method for synthesizingcrosslinking heterocycle oligomers, comprising the step of reacting in asuitable solvent about 2 moles of a crosslinking phenylimide carboxylicacid halide of the general formula: ##STR74## wherein i=1 or 2;φ=phenyl;X=halogen; and D=a divalent radical that includes hydrocarbonunsaturation, about n moles of a diacid halide, and n+1 moles of afour-functional compound of the general formula: ##STR75## wherein R=aradical such that each Y is on a separate carbon adjacent to anamine-substituted carbon; Y=--OH, --SH, or --NH₂ ; and n=an integergreater than or equal to 1, the reaction occurring at or below ambienttemperature in the presence of pyridine.
 27. The method of claim 26wherein R has the general formula: ##STR76## wherein M=--CO--, --S--,--O--, --SO₂ --, or --(CF₃)₂ C--.
 28. The product of the process ofclaim
 21. 29. An oligomer comprising the product of simultaneouslyreacting in a suitable solvent in the presence of pyridine under aninert atmosphere a mixture including:(a) 2 moles of a phenylimide acidchloride having the general formula: ##STR77## (b) n moles of a linearhydrocarbon moiety having terminal acid chloride functionalities and aplurality of aryl rings wherein at least two aryl rings are connected bya linkage selected from the group consisting of --SO₂ --, --S--, --CO--,and --(CF₃)₂ C--; and (c) n+1 moles of at least one four-functionalcompound selected from the group consisting of: ##STR78## wherein R isselected from the group consisting of radicals of the general formula:##STR79## M=--CO--, --S--, --O--, --SO₂ --, or --(CF₃)₂ C--; Z isselected from the group consisting of --OH, --SH, or --NH₂ ; Ph=phenyl;i=1 or 2; n is selected so that the oligomer has a formula weight ofbetween about 500 and about 30,000; Q is selected from the groupconsisting of: ##STR80## R₁ =lower alkyl, aryl, substituted aryl, loweralkoxy, or mixtures thereof; G=--SO₂ --, --S--, --O--, or --CH₂ --; j=0,1, or 2; Me=methyl; and T=allyl or methallyl.
 30. The oligomer of claim29 wherein the linear hydrocarbon moiety is selected from compounds ofthe general formula: ##STR81## wherein x=--O-- or --SO₂ --,andq=--(CF₃)₂ C--, --SO₂ --, --S--, or --CO--.
 31. The oligomer of claim29 wherein the Z=--OH.
 32. The oligomer of claim 29 wherein Z=--SH. 33.The oligomer of claim 29 wherein Z=--NH₂.